How to Manage Continuous Dyeing on Cotton
Leading Processes for Continuous Dyeing
Continuous dyeing of 100% cotton and cotton blends includes three main processes. Due to the market changes in lot sizes over the last 30 years, we saw modifications to these processes and how we incorporate them in operations. In the 70s and early 80s, it was common to see lots processed over 100,000 yards. Today most lots are less than 10,000 yards. The volumes changed, but the processes remain. Let’s review a brief explanation of each process:
Chemical Pad Steam (CPS):
The fabric is padded in the dye liquor and pre-dried. If we use a polyester and cotton blend, then it’s thermosoled. Next it’s padded through the alkali liquor, steamed, and ran through the rinsing and wash-off process.
Pad Dry Thermosol:
The fabric is padded through the pad or alkali liquor, pre-dried, thermosoled, and ran through the rinsing and wash-off process.
Cold Pad Batch Semi-Continuous Process:
We use this process for tubular and open width processing. The fabric is padded through the cold pad or alkali liquor, then batched on either A-frames or boxes at a low temperature for 12 – 24 hours. After batching, the fabric goes through the rinsing and wash-off processes.
The Chemical Pad Steam and Pad Dry Thermosol are usually ran by continuous processes. They will work equally well with semi-continuous.
Due to the smaller lot sizes, many customers have mini-ranges for optimum results.
Factors to Consider During Processing
Fabric must have uniform absorbency to insure proper wet pick-up, leveling, shade, and minimize back-to-face shading. At each step, be sure to cool the fabric before padding. This allows for dye and alkali pad liquor stability.
Design pads for the process you use to insure even wet pick-up and control side-to-side and side-to-center shading. To achieve good mix stability, control pad pan volume to a minimum level.
To prevent shading, pre-dryers, dryers and/or thermosol units must evenly dry fabric side-to-side, side-to-center, and back-to-face.
Rinse well to neutralize fabric before the wash-off at higher temperatures. Determine your final pH value for the fabric based on your finishing process.
Each factor is of equal importance. This is a brief overview, but can be useful when starting or looking for areas to improve.
Take Care When Making Dye Selections
Not all fiber reactive dye chemistries work for each process. Some are not recommended or suitable for any process.
There have been new developments in Multi-Functional Dyes such as Sorafix MF-CN that offer advantages over the older chemistries:
- Excellent reproducibility
- Less vulnerable to dye process parameters:
- Alkali Concentration
- Drying Temperature
- Steaming Temperature and Time
- Minimum tailing of pad liquor due to homogenous fixation behavior.
- Excellent wash-off properties.
- Higher light and wet fastness properties.
- High tinctorial value and solubility.
- More economical dyeing for deep shades; reduced production cost and less dye handling.
Dye selection is one of the key factors in controlling performance, cost, and meeting customer requirements.
If you are not satisfied with your current results, click the button below to request technical support and an introduction to the Sorafix MF-CN products.
About the Author: Ed Tessener
